Mechanical seal assemblies are extensively utilized in equipment to create a sealed relationship between a housing and a shaft which is rotatable relative thereto. The mechanical seal assembly typically includes a pair of annular seal rings which are respectively sealingly and nonrotatably coupled to the shaft and housing, and which have opposed flat seal faces which are normally urged toward one another to create a substantially sealed relationship between a high pressure zone disposed adjacent one radial edge of the seal faces, and a low or atmospheric pressure zone disposed adjacent the other radial edge thereof. It is conventional in numerous applications to form the assembly as a dry gas seal in that one of the seal faces is provided with a series of grooves therein for communication with the high pressure zone. These grooves facilitate creation of a gas film between the seal faces to minimize wear thereof and to likewise minimize overall frictional drag, such as during equipment start-up. Seal assemblies of this general type are well known, and examples thereof are disclosed in U.S. Pat. Nos. 3,499, 653 and 4,212,475.
In mechanical seals and specifically dry gas seals of the general type described above, at least one of the face rings is traditionally constructed of a hard but brittle material, frequently a carbide material such as silicon carbide. This brittle seal ring, which often is the rotating seal ring, must be interconnected to the shaft so as to be driven therewith. For this purpose the seal ring is traditionally mounted on a shaft sleeve arrangement which surrounds and nonrotatably couples to the shaft. It has been conventional to utilize drive pins which are fixed to the sleeve arrangement and engage openings or recesses in the face ring for effecting a nonrotatable connection therebetween. The use of drive pins for connection to the brittle seal ring, however, has proven to be a long-standing problem. Even though traditionally several such drive pins are coupled to the ring in circumferentially-spaced relationship therearound, nevertheless the rigidity of the drive pins and seal ring, when coupled with overall manufacturing tolerances, normally results in substantially all of the drive torque being transmitted from a single drive pin to the brittle seal ring, thereby resulting in a large concentration of stress where the loaded drive pin contacts the seal ring. This concentration of stress, coupled with impacts caused by clearances during starting and stopping conditions, often cause excessive stress on the seal ring which tend to cause cracking or breaking of the brittle seal ring. In fact, breaking of the brittle seal ring has been a long-standing problem, which problem has been difficult to solve inasmuch as the brittle material of the seal ring makes manufacture of the seal ring difficult.
Prior attempts to minimize the above problem have involved design variations which are known throughout the industry as "pinless" drives. Such pinless drives have, in one variation illustrated by U.S. Pat. No. 5,199, 172, involved forming substantially semi-cylindrical protrusions integral with an outer drive sleeve, with the protrusions being of a generally rounded configuration and cooperating with a similar rounded peripheral groove formed in the brittle seal ring. This prior attempted solution, however, is one which involves complex configurations for both the drive lug and the seal ring groove, and which still necessarily results in a hard or rigid drive lug engaged directly with the brittle seal ring.
Another attempt to resolve the above problem by means of a so-called "pinless" drive is illustrated by U.S. Pat. Nos. 4,586,719 and 5,076,589. The mechanical seal disclosed in these latter patents positions the rotating seal ring within a surrounding cuplike drive ring, the latter being coupled to the shaft for rotation therewith. To nonrotatably connect the seal ring to the drive ring, the seal ring is provided with flats spaced circumferentially around the outer periphery thereof, and wedgelike elastomeric keys are positioned on the flats for confinement in notches formed in the drive ring. This overall arrangement, however, involves not only a significant number of parts due to the number of elastomeric keys, but also requires creation of both flats on the seal ring and a plurality of circumferentially-spaced undercut grooves formed in the drive ring, with the overall arrangement being of complex and costly construction and assembly.
Another problem experienced with mechanical seals and particularly dry gas seals of the type described above relates to the maintaining of the rotating seal ring in concentric relationship relative to the shaft and its support sleeve. Many of the prior seals have possessed no capability for doing so, and have relied solely on the geometric confining relationship of the various cooperating parts. Others, such as the arrangement of U.S. Pat. No. 4,586,719 described above, have provided at least some resiliency which may be at least partially effective for centering the seal ring, although in most instance such centering effect itself is often restricted by other structural relationships of the seal.
Accordingly, it is an object of this invention to provide an improved mechanical seal, and particularly a dry gas seal, which incorporates therein an improved pinless drive for cooperation with one of the seal rings, preferably the rotating seal ring, so that the seal ring when constructed of a brittle material can be successfully keyed to or driven from a support member without creating the usual high stress or impact, whereby the life of the brittle seal ring can be greatly enhanced.
It is a further object of the invention to provide an improved mechanical seal, as aforesaid, with an improved resilient centering arrangement which cooperates with but is independent of the pinless drive so as to facilitate resilient centering of the brittle seal ring relative to its driving shaft or sleeve.
According to the present invention, in a preferred embodiment thereof, there is provided an improved mechanical seal having a pair of opposed seal rings, one nonrotatably connected to the housing, the other nonrotatably connected relative to a rotating shaft. The seal rings are resiliently relatively urged toward one another so that opposed flat faces thereon are normally maintained closely adjacent one another, with one of the faces in the preferred embodiment having a groove pattern which allows pressurized gas to be fed into and between the opposed seal faces to create a thin seal film or gap between the opposed seal faces. One of the seal rings, normally the rotating seal ring, is constructed of a brittle material such as a carbide material, and is positioned within and nonrotatably coupled to a sleeve arrangement which surrounds and is drivingly coupled to the shaft. The sleeve arrangement has an annular retaining flange which exteriorly surrounds the rotating seal ring, and a plurality of resilient pinless drives are disposed circumferentially therearound for drivingly coupling the retaining flange to the seal ring. Each resilient pinless drive employs a cylindrical coil spring which is confined within and between opposed grooves formed in the retaining flange and the seal ring for creating a resilient drive coupling therebetween.
In the improved mechanical seal, as aforesaid, the retaining flange also preferably provides resilient centering strips which are confined within grooves which extend circumferentially between the adjacent pinless resilient drives, with these resilient strips creating a resilient engagement with an outer annular surface of the seal ring over a majority of the exterior annular extent thereof, whereby the resilient strips effectively support and center the seal ring.
Other objects and purposes of the invention will be apparent to persons familiar with seal assemblies of this general type upon reading the following specification and inspecting the accompanying drawings.